The role of viruses or viral vaccines as possible teratogens is under investigation. Several arbovirus vaccines produced for human or animal use have been found to cause fetal death or severe central nervous system anomalies when inoculated intracerebrally into 100 day old Rhesus monkey fetuses. None of the control animals used in the studies developed malformations. Additional studies are in progress in which the pregnant animal rather than the fetus is infected much earlier in gestation. Project Number 02037-04 has been incorporated into Project Number NS 00972-05 ID, shown above.